[PATCHv3 03/13] xread_nonblock: add functionality to read from fds nonblockingly

[Stefan Beller <sbeller@google.com>]

This wrapper just restarts on EINTR, but not on EAGAIN like xread
does. This gives less guarantees on the actual reading rather than
on returning fast.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 git-compat-util.h |  1 +
 wrapper.c         | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/git-compat-util.h b/git-compat-util.h
index c6d391f..9ccea85 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -718,6 +718,7 @@ extern void *xcalloc(size_t nmemb, size_t size);
 extern void *xmmap(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 extern void *xmmap_gently(void *start, size_t length, int prot, int flags, int fd, off_t offset);
 extern ssize_t xread(int fd, void *buf, size_t len);
+extern ssize_t xread_nonblock(int fd, void *buf, size_t len);
 extern ssize_t xwrite(int fd, const void *buf, size_t len);
 extern ssize_t xpread(int fd, void *buf, size_t len, off_t offset);
 extern int xdup(int fd);
diff --git a/wrapper.c b/wrapper.c
index 50267a4..54ce231 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -223,6 +223,28 @@ ssize_t xread(int fd, void *buf, size_t len)
 }
 
 /*
+ * xread_nonblock() is the same a read(), but it automatically restarts read()
+ * interrupted operations (EINTR). xread_nonblock() DOES NOT GUARANTEE that
+ * "len" bytes is read even if the data is available.
+ */
+ssize_t xread_nonblock(int fd, void *buf, size_t len)
+{
+	ssize_t nr;
+	if (len > MAX_IO_SIZE)
+	    len = MAX_IO_SIZE;
+	while (1) {
+		nr = read(fd, buf, len);
+		if (nr < 0) {
+			if (errno == EINTR)
+				continue;
+			if (errno == EWOULDBLOCK)
+				errno = EAGAIN;
+		}
+		return nr;
+	}
+}
+
+/*
  * xwrite() is the same a write(), but it automatically restarts write()
  * operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
  * GUARANTEE that "len" bytes is written even if the operation is successful.
-- 
2.5.0.275.ge015d2a